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The "DD" in the name "VDD" refers to the drain terminal of an MOS transisitor. This may seen strange, since in the CMOS inverter VDD is actually connected to the source terminal of a PMOS transistor. However, CMOS logic circuits envoved from NMOS logic circuits, where the supply was connected to the drain of an NMOS transistor through a load resistor, and the name VDD stuck. Also note that ground is cometimes referred to as 'VSS' in CMOS and NMOS circuits. Some authors and most circuit manufactures use 'VCC' as the symbol for the CMOS supply voltage, since this name is used in TTL circuits, which historically preceded CMOS.4 f; V% j/ I* c. j$ w% _
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楼主
发表于 2010-11-3 14:53
